A transient in the Local Group dwarf irregular galaxy NGC 6822 (Barnards Galaxy) was discovered on 2017 August 2 and is only the second classical nova discovered in that galaxy. We conducted optical, near-ultraviolet, and X-ray follow-up observations of the eruption, the results of which we present here. This very fast nova had a peak $V$-band magnitude in the range $-7.41>M_V>-8.33$ mag, with decline times of $t_{2,V} = 8.1 pm 0.2$ d and $t_{3,V} = 15.2 pm 0.3$ d. The early- and late-time spectra are consistent with an Fe II spectral class. The H$alpha$ emission line initially has a full width at half-maximum intensity of $sim 2400$ km s$^{-1}$ - a moderately fast ejecta velocity for the class. The H$alpha$ line then narrows monotonically to $sim1800$ km s$^{-1}$ by 70 d post-eruption. The lack of a pre-eruption coincident source in archival Hubble Space Telescope imaging implies that the donor is a main sequence, or possibly subgiant, star. The relatively low peak luminosity and rapid decline hint that AT 2017fvz may be a faint and fast nova.
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